The invention relates to a short-circuiting device for an electric railway system having a conductor rail for supplying electric power to drive the vehicles. The function of the device is to provide a short circuit between a track rail and the conductor rail. The short circuiting device contains a first contact element providing a face to make contact with the track rail and a contact arm that is coupled to the contact element via a jointed connecting means and has a contact face for making contact with the conductor rail.
In contrast to interregional railway networks where power transfer takes place via overhead catenary systems, the transfer of power on underground railways (U-Lines) or City Lines normally takes place by way of a conductor rail. Such a conductor rail may e.g. be in the form of a rail mounted at the side of the track rails. The conductor rail may thereby be arranged in such a manner that the power collector makes sliding contact with the conductor rail from underneath, from the side or from above.
As a safety measure, when performing any kind of work on railway systems that have the above mentioned conductor rails, not only is the power supply to the conductor rail disconnected but a safety device is also installed i.e. a so called short-circuiting device which short-circuits the conductor acting as the positive pole with the rail acting as the minus pole—usually one of the track rails. This way, a short circuiting means, also called an earthing short circuit facility, creates an electrically conductive connection to conduct the electric current away when a handling error occurs, thus protecting the life of anyone involved.
To that end the above mentioned short circuiting device is installed before and after the place of work in order to protect the workplace and to prevent the flow of short circuit current on all sides.
A short circuiting device employed at present is made up of two arms that are coupled together via a hinge-type joint, whereby a first arm forms a contact arm which in the operating position lies horizontal and features a contact finger making contact with the conductor rail, and a second arm forms a base arm which lies vertical in the operating position and has a contact shoe resting on the rail track. In the operating position, the contact arm is pressed against the conductor rail by means of a tension spring which is hinged to the base arm and exercises a tensile force vertical to the conductor rail.
One of the disadvantages of the present-day short circuit devices is that their short circuit resistance is too low. As a rule the short circuit resistance of present-day short circuit devices lies at around 30 kA after a switch off time of 23 ms. The dimensioning of the electric equipment on railway systems is, however, often based on short circuits with power levels of 50 to 60 kA.
Short circuit devices, which are exposed to a higher level of current when a short circuit occurs, are as a rule destroyed or at least seriously damaged. The reason for this is e.g. that the cross-section of the conductor has been under-dimensioned and the conductive elements are thermally destroyed when the level of current flowing is too high. Further, circuit breakers of present-day design are normally catapulted away which, because of the risk of injury, is undesirable.